Grit, a concept proposed in the United States in 2007, has been widely applied across Eastern and Western cultures. Although emerging adulthood is a critical period for establishing self-identity and long-term goals, cross-cultural research on the item characteristics of the Short Grit Scale (Grit-S) during this period remains scarce. This study examines similarities and differences in Grit-S items between South Korea and the United States using item response theory's graded response model. Self-reported data from 4,231 individuals aged 18 ~ 25 (2,015 Korean, 2,216 U.S.) were analyzed. Results showed that items 3 and 4 of the Consistency of Interest subscale and items 5, 7, and 8 of the Perseverance of Effort subscale had high discrimination in both groups, supporting their validity for measuring goal orientation in emerging adulthood. In contrast, Item 6 of Perseverance of Effort (“Setbacks don't discourage me”) showed the lowest discrimination and poorly functioning category thresholds in both samples, suggesting revision. Additionally, Item 7 of Perseverance of Effort in the Korean sample was suitable mainly for low-perseverance respondents, indicating a need to better capture high-perseverance individuals. These findings highlight the importance of interpreting Grit-S items in light of cultural and developmental contexts.